Restriction of mobility in model liquid crystalline ionomers

Abstract

Model liquid crystalline ionomers have been analyzed by SAXS both in bulk and in toluene solution. These compounds are referred to as liquid crystalline halatosemitelechelic polystyrenes (LC HSTP's) and consist of low molecular weight polystyrene chains end-capped at one end by a sulfonate group associated to a mesogenic counterion. The results are in agreement with a microphase separation between the polymer chain and the mesogenic counterion. The main characteristic feature of the SAXS profile for the bulk material is the so-called ionic peak, whose position obeys a general law which is in favor of a rod-like organization of the multiplets and which shows that the polymer chains are stretched in the very close vicinity of the mesogenic core, in agreement with the Eisenberg, Hird and Moore model for ionomers. The thickness of this region of restricted mobility has been estimated to 1 nm, which is the order of magnitude of the persistence length of polystyrene. This very local restriction in mobility persists in toluene solution, in contrast to what is observed for the ω-Li-sulfonato-polystyrene precursors. The results also agree with an isotropic distribution of the multiplets in toluene.